HVAC systems typically have a plurality of return air ducts, each of which is provided with an air inlet covered by a hinged or removable louver or screen. The inlet also includes a frame for supporting a replaceable quadrilateral filter element. The typical replaceable filter element includes a cardboard frame and a fibrous mesh panel or similar filtration material which may be held in place by grids or large mesh screens. Also pleated filter panels have been used in replaceable filter elements.
The filter elements in HVAC systems are replaced periodically in order to insure effective filtration of air. Replacement of the filter elements several times a year results in a considerable expense to occupants and owners of buildings.
Heretofore a variety of fluid filters have been heretofore been proposed. Pleated air filters are disclosed in a U.S. Pat. No. 4,199,387 issued Apr. 22, 1980 to S. M. Hladik for an Air Filter Fabrication Method, in U.S. Pat. No. 4,042,358 issued Aug. 16, 1977 to S. H. Frohmader for a Filter Media and in U.S. Pat. No. 5,167,740 issued Dec. 1, 1992 to U. Michaelis et al. for a Method of Making a Filter Element Insert of Nonwoven Material in the Form of a Pleated Pack. Filter elements for liquids are disclosed in U.S. Pat. No. 4,629,474 issued to D. I. Thornton for a Thermally Formed Filter and in U.S. Pat. No. 5,456,836 issued Oct. 10, 1995 to A. B. Jeffery et al. for a High Efficiency, Self-Supporting Filter Element Make From Fibers.